Sodium-ion battery preparation method adopting stepped temperature formation

Abstract

The invention relates to the technical field of sodium ion battery preparation, in particular to a sodium ion battery preparation method adopting stepped temperature formation, and the stepped temperature formation comprises the following specific steps: (A1) carrying out first formation in a battery open-circuit voltage range of-2.92 V (vs.Na + / Na) and at the formation temperature of-15 DEG C, and standing at normal temperature after the formation is finished; (A2) carrying out secondary formation under the condition that the open-circuit voltage of the battery is-2.95 V (vs.Na + / Na) voltage range and the formation temperature is-5 DEG C, and standing at normal temperature after the formation is finished; and (A3) carrying out third formation under the condition that the open-circuit voltage of the battery is-4.0 V (vs.Na + / Na) voltage range and the formation temperature is 5 DEG C, and standing at normal temperature after the formation is finished. According to the invention, the formation temperature is accurately controlled, the decomposition reaction of the additive on the surface of the copper foil is promoted, an electrode / electrolyte interfacial film rich in inorganic components and S-containing organic components is generated, the stability of the interface is improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery preparation, and in particular to a method for preparing a sodium ion battery using step temperature formation. Background Art

[0002] Against the backdrop of energy transformation and sustainable development, the new energy industry is booming at an unprecedented pace. As a core component in the new energy field, technological innovation in energy storage equipment is particularly critical. Lithium-ion batteries, with their high energy density, long cycle life and mature technology system, have long dominated the energy storage equipment market. However, with the rapid expansion of the global electric vehicle market and the surge in demand for energy storage systems, the scarcity and uneven distribution of lithium resources have become increasingly prominent, which has directly led to rising costs of lithium-ion batteries and instability in the supply chain.

[0003] In order to meet this challenge, the scientific research and industrial communities have turned their attention to sodium-ion batteries, a new energy storage technology with great potential. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, both of which store and release electrical energy through the embedding and de-embedding of lithium or sodium ions between the positive and negative electrodes. However, compared with lithium resources, sodium resources are more abundant in the earth's crust, which gives sodium-ion batteries a significant advantage in raw material costs and reduces dependence on rare metal resources.

[0004] Traditional lithium-ion batteries require negative electrode materials to receive lithium ions, while negative electrode-free sodium-ion batteries omit this step and only use copper foil as the current collector. This design not only simplifies the battery structure and reduces production costs, but also improves the energy density and safety of the battery. However, negative electrode-free sodium-ion batteries also face some technical difficulties during the formation process, especially the stability of the electrode / electrolyte interface and the generation of sodium dendrites. These problems directly affect the performance and life of the battery, and have become a key factor restricting the large-scale application of negative electrode-free sodium-ion batteries. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art and improve the performance and life of a negative electrode-free sodium ion battery, the present invention provides a method for preparing a sodium ion battery using a stepped temperature formation.

[0006] To achieve the above object, the present invention discloses a method for preparing a sodium ion battery using step temperature formation, comprising the following steps:

[0007] (S1) preparing positive and negative electrodes of the battery to form a soft-pack battery;

[0008] (S2) preparing an electrolyte and injecting the electrolyte into the soft pack battery;

[0009] (S3) high-temperature soaking the soft-pack battery injected with electrolyte to ensure that the electrolyte fully soaks the battery cell;

[0010] (S4) Step temperature formation:

[0011] (A1) The first formation is performed under the conditions of a battery open circuit voltage range of -2.92 V (vs. Na+ / Na) and a formation temperature of -15°C. After the formation is completed, the battery is allowed to stand at room temperature;

[0012] (A2) performing a second formation at a battery open circuit voltage range of -2.95 V (vs. Na+ / Na) and a formation temperature of -5°C, and after the formation is completed, allowing the battery to stand at room temperature;

[0013] (A3) performing a third formation at a battery open circuit voltage range of -4.0 V (vs. Na+ / Na) and a formation temperature of 5° C., and after the formation is completed, allowing the battery to stand at room temperature;

[0014] (S5) Normal temperature formation: charging to 4.0 V at 0.025 C constant current at 25°C;

[0015] (S6) releasing the gas in the formed soft-pack battery and performing secondary packaging on the side of the soft-pack battery;

[0016] (S7) Aging.

[0017] Further, in step (S1), Na 3 V 2 (PO 4 ) 3 (NVP) system material is used as the positive electrode of the sodium ion battery, and copper foil is used as the negative electrode of the sodium ion battery.

[0018] Preferably, Na 3 V 2 (PO 4 ) 3 The preparation method of the (NVP) system material is: using NVP as the active material, using Super P as the first conductive agent, using CNT as the second conductive agent, and using PVDF as the binder, wherein the mass ratio of NVP:Super P:CNT:PVDF=95:1:1:3, and then adding solvent NMP, the solvent NMP accounts for 40% of the total slurry, and coating the configured slurry on the surface of carbon-coated aluminum foil.

[0019] Furthermore, the components of the electrolyte include A, B, and C, wherein A is sodium hexafluorophosphate (NaPF 6), B is sodium difluorobis(oxalyl)phosphate (NaDODFP), and C is a mixture of fluoroethylene carbonate (FEC), 3-propane sulfonate (PS) and dimethyl carbonate (DMC).

[0020] Preferably, NaPF 6 The concentration is between 1.5 and 3.0 mol·L-1, the NaDODFP concentration is between 0.1 and 0.3 mol·L-1, the FEC volume fraction is between 5 vol% and 10 vol%, and the PS volume fraction is between 2 vol% and 5 vol%.

[0021] Preferably, the electrolyte injection coefficient is 2.5 g / Ah.

[0022] Furthermore, in step (S3), high temperature soaking refers to placing the soft-pack battery at 45° C. for 12-24 hours.

[0023] Furthermore, high temperature aging refers to placing the soft-pack battery at 35-45°C for 24-72 hours.

[0024] The present invention has the following technical effects:

[0025] (1) Improving the interfacial stability of negative electrode-free sodium ion batteries

[0026] In the formation process of anode-free sodium-ion batteries, the stability of the electrode / electrolyte interface has a crucial impact on the performance and life of the battery. The step temperature formation method proposed in this patent effectively promotes the decomposition reaction of the additive on the copper foil surface by setting different formation temperatures in different voltage ranges, and generates an electrode / electrolyte interface film rich in inorganic components and organic components containing S, such as the attached Figure 2 To Attachment Figure 5 This interfacial film can significantly reduce the impedance of the electrode / electrolyte interface (see Figure 6 To Attachment Figure 7 As shown in the figure), the stability of the interface is improved, thereby extending the service life of the battery. Figure 8 shown.

[0027] (2) Inhibit the formation of sodium dendrites and improve the safety performance of batteries

[0028] The formation of sodium dendrites is an important problem faced by negative electrode-free sodium ion batteries during the charging and discharging process. It may cause battery short circuit, thus affecting the safety performance of the battery. The step temperature formation method of this patent promotes the stable formation of the interface film by optimizing the formation temperature and voltage range, thereby effectively inhibiting the formation of sodium dendrites. This greatly improves the safety performance of the battery and prevents the short circuit problem caused by sodium dendrites piercing the diaphragm, such as the attached Figure 8 shown.

[0029] (3) Simplify battery structure and reduce production costs

[0030] The cathode-free sodium-ion battery uses copper foil as the current collector, omitting the use of the cathode material, thereby simplifying the battery structure and reducing production costs. The step temperature formation method of this patent further optimizes the battery formation strategy, making the battery manufacturing process more efficient and cost-effective. At the same time, since the cathode material is omitted, the use of raw materials is also reduced, which is conducive to resource conservation and environmental protection.

[0031] (4) Improve battery performance and promote the development of new energy industry

[0032] By adopting the step temperature formation method of this patent, the negative electrode-free sodium ion battery shows excellent performance in terms of energy density, cycle stability and safety performance. Figure 8 This not only provides new energy solutions for electric vehicles, portable devices and other fields, but also provides new impetus for the development of the new energy industry. The proposal of this patent is expected to promote the commercialization of negative electrode-free sodium ion battery technology and make important contributions to energy transformation and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The charge specific capacity-voltage curve of the first charge of the negative electrode-free sodium ion battery;

[0034] Figure 2 XPS diagram of SEI film on copper foil surface - S2p diagram formed at room temperature;

[0035] Figure 3 XPS graph of SEI film on copper foil surface - F1s graph formed at room temperature;

[0036] Figure 4 XPS diagram of SEI film on copper foil surface - S2p diagram transformed by step temperature;

[0037] Figure 5 XPS diagram of SEI film on copper foil surface - F1s diagram transformed by step temperature;

[0038] Figure 6 This is the EIS diagram of the negative electrode-free sodium ion battery after formation at room temperature;

[0039] Figure 7 This is the EIS diagram of the negative electrode-free sodium-ion battery after step temperature formation;

[0040] Figure 8 This is the long cycle performance diagram of the negative electrode-free sodium ion battery formed at room temperature and step temperature; DETAILED DESCRIPTION

[0041] The principles and features of the present invention are described below in conjunction with embodiments; the examples given are only used to explain the present invention; they are not used to limit the scope of the present invention.

[0042] A method for preparing a sodium ion battery using step temperature formation comprises the following steps:

[0043] (S1) Prepare the positive and negative electrodes of the battery to form a soft pack battery. 3 V 2 (PO 4 ) 3 (NVP) system materials are used as the positive electrode of the sodium ion battery; the negative electrode does not use any materials, only copper foil is used as the negative electrode of the sodium ion battery. The preparation method of the positive electrode of the sodium ion battery is: using NVP as the active material, using Super P as the first conductive agent, using CNT as the second conductive agent, and using PVDF as the binder, wherein the mass ratio NVP: Super P: CNT: PVDF = 95: 1: 1: 3, the total mass of the positive electrode is 47.368g, of which NVP is 45g, and finally adding an appropriate amount of solvent NMP (accounting for 40% of the total weight of the slurry) to prepare a slurry and coat it on the surface of the carbon-coated aluminum foil as the positive electrode of the sodium ion battery.

[0044] (S2) preparing an electrolyte and injecting the electrolyte into the soft pack battery. The components of the electrolyte include A, B, and C, wherein the volume ratio of A:B:C is 7:3:90; wherein A is sodium hexafluorophosphate (NaPF 6 ), B is sodium difluorobis(oxalyl)phosphate (NaDODFP), C is a mixture of fluoroethylene carbonate (FEC), 3-propane sulfonate (PS) and dimethyl carbonate (DMC), and the volume ratio of FEC:PS:DMC is 7:3:90. NaPF 6 The concentration is between 1.5 and 3.0 mol·L-1, the NaDODFP concentration is between 0.1 and 0.3 mol·L-1, the FEC volume fraction is between 5 vol% and 10 vol%, and the PS volume fraction is between 2 vol% and 5 vol%. Specifically, weigh 336 g of NaPF 6 53.6 g of NaDODFP was dissolved in 1000 mL of FEC / PS / DMC mixed solvent and placed in an ultrasonic cleaner for 10 min to promote the NaPF 6 The component contents of each embodiment are shown in Table 1. After the configuration is completed, the battery soft pack is injected with a liquid injection coefficient of 2.5 g / Ah.

[0045] Table 1 Component contents of each embodiment and capacity retention rate after 300 cycles

[0046]

[0047]

[0048] (S3) The soft-pack battery injected with the electrolyte is subjected to high-temperature soaking. The high-temperature soaking condition is 45° C. and allowed to stand for 24 hours to ensure that the electrolyte fully soaks the battery cell.

[0049] (S4) Step temperature formation, the specific method is:

[0050] (A1) The first formation is performed under the conditions of a battery open circuit voltage range of -2.92V (vs. Na+ / Na) and a formation temperature of -15°C. After the formation is completed, the battery is allowed to stand at room temperature (25°C) for 15 minutes before proceeding to the next step;

[0051] (A2) Performing a second formation at a battery open circuit voltage range of -2.95 V (vs. Na+ / Na) and a formation temperature of -5°C. After the formation is completed, standing at room temperature (25°C) for 15 minutes before proceeding to the next step;

[0052] (A3) The third formation was carried out under the conditions of a battery open circuit voltage range of -4.0 V (vs. Na+ / Na) and a formation temperature of 5°C. After the formation was completed, the battery was allowed to stand at room temperature (25°C) for 60 minutes.

[0053] (S5) Normal temperature formation: at 25°C, the battery is charged to 4.0 V using a constant current of 0.025C.

[0054] (S6) releasing the gas in the formed soft-pack battery and performing secondary packaging on the side of the soft-pack battery.

[0055] (S7) Aging: The soft-pack battery is placed at 45° C. for 48 hours for high-temperature aging to obtain a finished soft-pack battery.

[0056] (S8) The finished soft-pack battery is placed under 25° C. for a long cycle test, with a test voltage range of 2.0-4.0 V and a cycle rate of 0.5C.

[0057] The charge capacity-voltage curve of the first charge of the negative electrode-free sodium ion battery prepared by taking the components of the electrolyte in Example 2 as an example is shown in the attached figure. Figure 1 As shown. The additives (FEC and NaDODFP) mainly decompose in the voltage range of 2.75-2.95V. Based on the characteristic morphology of the voltage curve, we subdivide the front part of the charging process into two stages: 2.75-2.92V stage and 2.92-2.95V stage. In these two stages, the formation temperature is set to -15℃ and -5℃ respectively, while the formation temperature of the last stage is increased to 5℃.

[0058] In the first two stages, since the decomposition reaction of the additive is an exothermic reaction, we adopted a step-by-step low-temperature induction strategy to promote its decomposition. This method helps to form an interface film rich in inorganic components and S-containing organic components at the electrode / electrolyte interface on the copper foil surface. Among them, the inorganic component can increase the migration rate of sodium ions at the interface, while the S-containing organic component enhances the adhesion between the interface and the copper foil due to its sufficient flexibility. The final result of this series of reactions and strategies is a significant improvement in the stability of the interface.

[0059] This stable interface exhibits excellent performance in inhibiting the precipitation of sodium dendrites, providing a solid foundation for the long-term stable cycle of the battery.

[0060] Figures 2 to 5 This shows that the step temperature formation method promotes the decomposition of additives, which greatly increases the content of inorganic components and S-containing organic components in the SEI film, providing a solid foundation for improving the battery cycle life and stability.

[0061] Figure 6 This is the ESI diagram of a negative electrode-free sodium-ion battery formed at room temperature. Figure 7 This is the ESI diagram of a negative electrode-free sodium-ion battery using a step temperature formation method. By comparison, it can be seen that the step temperature formation causes the interface to contain more inorganic components, resulting in a significant decrease in the impedance of the battery.

[0062] Figure 8 The long cycle performance diagram of the negative electrode-free sodium ion battery using room temperature formation and step temperature formation is shown in the figure. Through comparison, it can be shown that due to the difference in interface properties, the long cycle life of the negative electrode-free sodium ion battery using step temperature formation has been significantly improved, and the battery capacity has no obvious decrease even after 300 cycles.

[0063] The present invention promotes the decomposition reaction of the additive on the surface of the copper foil by precisely controlling the formation temperature, thereby generating an electrode / electrolyte interface film rich in inorganic components and organic components containing S. This interface film can effectively reduce the impedance of the electrode / electrolyte interface, improve the stability of the interface, and thus extend the service life of the battery.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a sodium ion battery using step temperature formation, characterized in that: The following steps are involved: (S1) preparing positive and negative electrodes of the battery to form a soft-pack battery; (S2) preparing an electrolyte and injecting the electrolyte into the soft pack battery; (S3) high-temperature soaking the soft-pack battery injected with electrolyte to ensure that the electrolyte fully soaks the battery cell; (S4) Step temperature formation: (A1) The first formation is performed under the conditions of a battery open circuit voltage range of -2.92 V (vs. Na+ / Na) and a formation temperature of -15°C. After the formation is completed, the battery is allowed to stand at room temperature; (A2) performing a second formation at a battery open circuit voltage range of -2.95 V (vs. Na+ / Na) and a formation temperature of -5°C, and after the formation is completed, allowing the battery to stand at room temperature; (A3) performing a third formation at a battery open circuit voltage range of -4.0 V (vs. Na+ / Na) and a formation temperature of 5° C., and after the formation is completed, allowing the battery to stand at room temperature; (S5) Normal temperature formation: charging to 4.0 V at 0.025 C constant current at 25°C; (S6) releasing the gas in the formed soft-pack battery and performing secondary packaging on the side of the soft-pack battery; (S7) Aging.

2. The method for preparing a sodium ion battery using step temperature formation according to claim 1, characterized in that: In step (S1), Na3V2(PO4)3(NVP) system material is used as the positive electrode of the sodium ion battery, and copper foil is used as the negative electrode of the sodium ion battery.

3. The method for preparing a sodium ion battery using step temperature formation according to claim 2, characterized in that: The preparation method of the positive electrode of the sodium ion battery is as follows: using NVP as an active material, using Super P as a first conductive agent, using CNT as a second conductive agent, and using PVDF as a binder, wherein the mass ratio is NVP:Super P:CNT:PVDF=95:1:1:3; then adding solvent NMP, wherein the solvent NMP accounts for 40% of the total slurry; and coating the configured slurry on the surface of a carbon-coated aluminum foil.

4. The method for preparing a sodium ion battery using step temperature formation according to claim 1, characterized in that: The components of the electrolyte include A, B, and C, wherein A is sodium hexafluorophosphate (NaPF6), B is sodium difluorobis(oxalyl)phosphate (NaDODFP), and C is a mixture of fluoroethylene carbonate (FEC), 3-propane sulfonate (PS), and dimethyl carbonate (DMC).

5. The method for preparing a sodium ion battery using step temperature formation according to claim 4, characterized in that: Sodium hexafluorophosphate (NaPF6) concentration is between 1.5 and 3.0 mol·L -1 , sodium difluorobis(oxalyl)phosphate (NaDODFP) concentration is between 0.1 and 0.3 mol·L -1 The volume fraction of fluoroethylene carbonate (FEC) is between 5 vol% and 10 vol%, the volume fraction of 3-propane sulfonate (PS) is between 2 vol% and 5 vol%, and the rest is dimethyl carbonate (DMC).

6. The method for preparing a sodium ion battery using step temperature formation according to claim 5, characterized in that: The electrolyte injection coefficient is 2.5g / Ah.

7. The method for preparing a sodium ion battery using step temperature formation according to claim 1, characterized in that: In step (S3), high temperature soaking refers to placing the soft-pack battery at 35-45°C for 12-24 hours.

8. The method for preparing a sodium ion battery using step temperature formation according to claim 1, characterized in that: In step (S7), high temperature aging refers to placing the soft-pack battery at 35-45° C. for 24-72 hours.

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